Something that was deeply offensive to most of the cultures the Vikings encountered was that Vikings didn't worry too much about fidelity, even the women could shag around, and their husbands happily accepted the children as their own even if they knew they weren't the father.

The reason was quite simple. Keeping a child alive was difficult back then so any child that survived was a miracle, and people wanted big families, so if your wife had a child it was your right as the husband to keep it. The other loser could mob around with one child less to his name.